I have both of them and i prefer the Dingoo A320 over the others.
The Dingoo Tech A330 has clicky, problematic buttons most of the time, but same exact software and interface as the A320.
I like the PSP style form factor, and haven't tried using the controller with it, but i've read that it only works with particular games, kind of ruining your fun if you have plans to play a game and it doesn't work on it...
Then there's the Gemei A330, great, improved form factor over the A320, however, it is still way behind in emulation quality and is still buggy, unless you go with one of the custom firmwares out there that tend to either not work correctly or just plain brick your unit.
The A320, amongst the above three, is going to be the bang for your buck, especially if you take care of it.